Nickel-base alloy

ABSTRACT

The invention is a class of nickel-base alloys for gas turbine applications, comprising, by weight, about 13.7 to about 14.3 percent chromium, about 5.0 to about 10.0 percent cobalt, about 3.5 to about 5.2 percent tungsten, about 2.8 to about 5.2 percent titanium, about 2.8 to about 4.6 percent aluminum, about 0.0 to about 3.5 percent tantalum, about 1.0 to about 1.7 percent molybdenum, about 0.08 to about 0.13 percent carbon, about 0.005 to about 0.02 percent boron, about 0.0 to about 1.5 percent niobium, about 0.0 to about 2.5 percent hafnium, about 0.0 to about 0.04 percent zirconium, and the balance substantially nickel. The nickel-base alloys may be provided in the form of useful articles of manufacture, and which possess a unique combination of mechanical properties, microstructural stability, resistance to localized pitting and hot corrosion in high temperature corrosive environments, and high yields during the initial forming process as well as post-forming manufacturing and repair processes.

BACKGROUND OF THE INVENTION

The present invention generally relates to nickel-base alloys for gasturbine applications, which possess a unique combination of mechanicalproperties, microstructural stability, and resistance to localizedpitting and hot corrosion. More specifically, the invention relates to aclass of nickel-base alloys having very low fractions of Eta phase andsegregated titanium; resulting in improved yield, manufacturability, andrepairability of articles formed therefrom.

The present invention is an improvement to the class of alloys disclosedand claimed in U.S. Pat. No. 6,416,596 B1, issued Jul. 9, 2002 to JohnH. Wood et al.; which was an improvement to the class of alloysdisclosed and claimed in U.S. Pat. No. 3,615,376, issued Oct. 26, 1971to Earl W. Ross. Both patents are assigned to the assignee hereof. Theinvention retains the advantageous attributes of those alloys; includinghigh strength and ductility, high resistance to creep and fatigue,excellent microstructural stability, and high resistance to localizedpitting and hot corrosion in high temperature corrosive environments.This unique combination of properties makes those alloys attractive foruse in gas turbines.

However, an attribute of the alloys disclosed and claimed in U.S. Pat.No. 6,416,596 (hereinafter referred to as the “reference alloys”) is thepresence of “Eta” phase, a hexagonal close-packed form of theintermetallic Ni₃Ti, as well as segregated titanium metal in thesolidified alloy. During alloy solidification, titanium has a strongtendency to be rejected from the liquid side of the solid/liquidinterface, resulting in the segregation (local enrichment) of titaniumin the solidification front and promoting the formation of Eta in thelast solidified liquid. The segregation of titanium also reduces thesolidus temperature, increasing the fraction of γ/ γ′ eutectic phasesand resulting micro-shrinkages in the solidified alloy. The Eta phase,in particular, may cause certain articles formed from those alloys to berejected during the initial forming process, as well as post-formingmanufacturing and repair processes. In addition, the presence of Etaphase may result in degradation of the alloy's mechanical propertiesduring service exposure.

It was learned from experimental evaluations that the fractions of bothEta phase and segregated titanium in the solidified alloy are reduced bychanging the alloy composition in such a manner that the content oftitanium is reduced, and the ratio of aluminum to titanium is increased,relative to the composition of the reference alloys. This results fromatom partitioning in the solid/liquid interface during alloysolidification, causing a reduction in the fraction of the γ/ γ′eutectic phase in the solidified alloy. It was also learned in theseevaluations that the Eta phase is further reduced by changing the alloycomposition in such a manner that the content of tantalum is increased,and the ratio of aluminum to tantalum is reduced, relative to thecomposition of the reference alloys. Tantalum was known to stabilize thegamma prime (γ′) phase (Ni₃Al), further reducing the availability oftitanium in the alloy.

It was also known that advantageous amounts of gamma prime (γ′) phaseare retained when the content of tantalum is reduced and the content ofniobium is increased, such that niobium may be entirely substituted fortantalum if desired, as taught in U.S. Pat. No. 6,902,633 B2, issuedJun. 7, 2005 to Warren T. King et al. and assigned to the assigneehereof; and U.S. Pat. Appl. Publ. No. 2007/0095441 A1, published May 3,2007 by Liang Jiang et al. and assigned to the assignee hereof.

It was also known that increasing the contents of tantalum and tungstenrelative to the reference alloys result in improved mechanicalproperties through a combination of solid solution and precipitationstrengthening. These changes produced alloys having tensile strength,yield strength, ductility, and Low Cycle Fatigue (LCF) strengthgenerally comparable to the reference alloys; as well as improved creepstrength and lower machining energy relative to the reference alloys forcertain embodiments of the present invention.

The totality of these changes produced additional benefits. For example,the alloys exhibit a narrow solidification range (defined as thedifference in temperature between the liquidus and solidus of the alloy)and the microstructures of the solidified alloys exhibit a finer γ/γ′eutectic and carbide structure than the microstructures of the referencealloys.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a class of nickel-base alloys for gasturbine applications, and useful articles of manufacture formedtherefrom, which possess a unique combination of mechanical properties,microstructural stability, resistance to localized pitting and hotcorrosion in high temperature corrosive environments, and high yieldsduring the initial forming process as well as post-forming manufacturingand repair processes. The invention is further characterized by havingvery low fractions of Eta phase and segregated Titanium in thesolidified nickel-base alloys.

According to a particular embodiment of the present invention, thenickel-base alloy comprises, by weight, about 13.7 to about 14.3 percentchromium, about 5.0 to about 10.0 percent cobalt, about 3.5 to about 5.2percent tungsten, about 2.8 to about 5.2 percent titanium, about 2.8 toabout 4.6 percent aluminum, about 0.0 to about 3.5 percent tantalum,about 1.0 to about 1.7 percent molybdenum, about 0.08 to about 0.13percent carbon, about 0.005 to about 0.02 percent boron, about 0.0 toabout 1.5 percent niobium, about 0.0 to about 2.5 percent hafnium, about0.0 to about 0.04 percent zirconium, and the balance substantiallynickel.

According to another embodiment of the present invention, wherein theform of the invention is an article of manufacture; the nickel-basealloy comprises, by weight, about 13.7 to about 14.3 percent chromium,about 5.0 to about 10.0 percent cobalt, about 3.5 to about 5.2 percenttungsten, about 2.8 to about 5.2 percent titanium, about 2.8 to about4.6 percent aluminum, about 0.0 to about 3.5 percent tantalum, about 1.0to about 1.7 percent molybdenum, about 0.08 to about 0.13 percentcarbon, about 0.005 to about 0.02 percent boron, about 0.0 to about 1.5percent niobium, about 0.0 to about 2.5 percent hafnium, about 0.0 toabout 0.04 percent zirconium, and the balance substantially nickel.

Other objects and advantages of the present invention will be betterappreciated from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments are described with referenceto the following drawings.

FIG. 1 is a photomicrograph of Alloy 1, as embodied by the invention.

FIG. 2 is a photomicrograph of Alloy 2, as embodied by the invention.

FIG. 3 is a photomicrograph of Alloy 3, as embodied by the invention.

FIG. 4 is a photomicrograph of Alloy 4, as embodied by the invention.

FIG. 5 is a photomicrograph of Alloy 5, as embodied by the invention.

FIG. 6 is a photomicrograph of Alloy 6, as embodied by the invention.

FIG. 7 is a photomicrograph of Alloy 7, as embodied by the invention.

FIG. 8 is a plot showing normalized tensile strength of Alloys 1 to 4,measured at 20° C. (68° F.) and 760° C. (1400° F.), shown as thefraction of the average tensile strength of the reference alloys atthose temperatures.

FIG. 9 is a plot showing normalized creep life of Alloys 1 to 4, interms of the times to 1.0% strain at 732° C. (1350° F.), shown as thefraction of the average creep life of the reference alloys at the samestrain and temperature.

FIG. 10 is a plot showing the machining energy (in Joules) required forAlloys 1 and 2 during a milling operation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention was the result of an investigation to develop aclass of nickel-base alloys for gas turbine applications, and usefularticles of manufacture formed therefrom, which possess a uniquecombination of mechanical properties, microstructural stability,resistance to localized pitting and hot corrosion in high temperaturecorrosive environments, and high yields during the initial formingprocess as well as post-forming manufacturing and repair processes. Theinvention is further characterized by having very low fractions of Etaphase and segregated Titanium in the solidified nickel-base alloys.

According to a particular embodiment of the present invention, thenickel-base alloy comprises, by weight, about 13.7 to about 14.3 percentchromium, about 5.0 to about 10.0 percent cobalt, about 3.5 to about 5.2percent tungsten, about 2.8 to about 5.2 percent titanium, about 2.8 toabout 4.6 percent aluminum, about 0.0 to about 3.5 percent tantalum,about 1.0 to about 1.7 percent molybdenum, about 0.08 to about 0.13percent carbon, about 0.005 to about 0.02 percent boron, about 0.0 toabout 1.5 percent niobium, about 0.0 to about 2.5 percent hafnium, about0.0 to about 0.04 percent zirconium, and the balance substantiallynickel.

According to another embodiment of the present invention, thenickel-base alloy is characterized by having very low fractions of Etaphase and segregated Titanium; and comprises, by weight, about 13.7 toabout 14.3 percent chromium, about 5.0 to about 10.0 percent cobalt,about 3.5 to about 5.2 percent tungsten, about 2.8 to about 5.2 percenttitanium, about 2.8 to about 4.6 percent aluminum, about 0.0 to about3.5 percent tantalum, about 1.0 to about 1.7 percent molybdenum, about0.08 to about 0.13 percent carbon, about 0.005 to about 0.02 percentboron, about 0.0 to about 1.5 percent niobium, about 0.0 to about 2.5percent hafnium, about 0.0 to about 0.04 percent zirconium, and thebalance substantially nickel.

According to another embodiment of the present invention, thenickel-base alloy comprises, by weight, about 13.9 percent chromium,about 9.5 percent cobalt, about 4.5 percent tungsten, about 4.2 percenttitanium, about 3.7 percent aluminum, about 3.4 percent tantalum, about1.6 percent molybdenum, about 0.1 percent carbon, about 0.01 percentboron, less than 0.01 percent zirconium, and the balance substantiallynickel.

According to yet another embodiment of the present invention, thenickel-base alloy comprises, by weight, about 13.9 percent chromium,about 9.5 percent cobalt, about 4.2 percent tungsten, about 3.7 percenttitanium, about 3.7 percent aluminum, about 3.2 percent tantalum, about1.5 percent molybdenum, about 0.1 percent carbon, about 0.01 percentboron, about 0.002 percent zirconium, and the balance substantiallynickel.

According to embodiments of the present invention, wherein the form ofthe invention is an article of manufacture, the article may be formed bya casting method comprising the following steps: (1) preparing an ingotof the composition in the amounts stated above, (2) remelting the ingotand casting it to a form of the size and shape of the desired article,(3) heat treating the article in a suitable atmosphere and in accordancewith a suitable time and temperature schedule, and (4) coating thearticle, if desired, with a suitable material for thermal orenvironmental protection. The grain structure of the cast articles maybe either equiaxed (having no preferred orientation), directionallysolidified (having a preferred orientation), or single crystal (havingno grain boundaries). The article may be a gas turbine bucket or otherform of rotating airfoil, or a gas turbine nozzle or other form ofstationary airfoil, or another gas turbine component, that is located inthe gas turbine hot section and designed in such a manner as to takeadvantage of the beneficial properties of the alloy.

According to a particular embodiment of the present invention, whereinthe form of the invention is an article of manufacture, the nickel-basealloy comprises, by weight, about 13.7 to about 14.3 percent chromium,about 5.0 to about 10.0 percent cobalt, about 3.5 to about 5.2 percenttungsten, about 2.8 to about 5.2 percent titanium, about 2.8 to about4.6 percent aluminum, about 0.0 to about 3.5 percent tantalum, about 1.0to about 1.7 percent molybdenum, about 0.08 to about 0.13 percentcarbon, about 0.005 to about 0.02 percent boron, about 0.0 to about 1.5percent niobium, about 0.0 to about 2.5 percent hafnium, about 0.0 toabout 0.04 percent zirconium, and the balance substantially nickel; andthe article may be formed by a casting method that produces gas turbineairfoils or other components having either an equiaxed, directionallysolidified, or single crystal grain structure.

According to another embodiment of the present invention, wherein theform of the invention is an article of manufacture, the nickel-basealloy comprises, by weight, about 13.9 percent chromium, about 9.5percent cobalt, about 4.5 percent tungsten, about 4.2 percent titanium,about 3.7 percent aluminum, about 3.4 percent tantalum, about 1.6percent molybdenum, about 0.1 percent carbon, about 0.01 percent boron,less than 0.01 percent zirconium, and the balance substantially nickel;and the article may be formed by a casting method that produces gasturbine airfoils or other components having an equiaxed grain structure.

According to yet another embodiment of the present invention, whereinthe form of the invention is an article of manufacture, the nickel-basealloy comprises, by weight, about 13.9 percent chromium, about 9.5percent cobalt, about 4.2 percent tungsten, about 3.7 percent titanium,about 3.7 percent aluminum, about 3.2 percent tantalum, about 1.5percent molybdenum, about 0.1 percent carbon, about 0.01 percent boron,about 0.002 percent zirconium, and the balance substantially nickel; andthe article may be formed by a casting method that produces gas turbineairfoils or other components having a directionally solidified grainstructure.

A feature of embodiments of the present invention is that the contentsof aluminum and titanium and their relative ratios may be adjusted insuch a manner that reduces the fractions of the γ/γ′ eutectic phase, Etaphase, and segregated titanium that form during alloy solidification.For example, the solidified alloys are substantially free of Eta phasewhen the ratio of aluminum to titanium is between about 0.8 and about1.0, by weight. A further benefit is a strengthening effect that may bedue to an increase in γ′ phase in the γ matrix.

Another feature of embodiments of the present invention is that thecontents of aluminum and tantalum and their relative ratios may beadjusted in such a manner that further reduces the formation of Etaphase, while maintaining the fraction of γ′ phase, in the solidifiedalloy. For example, the solidified alloys are substantially free of Etaphase when the ratio of aluminum to tantalum is between about 0.9 andabout 1.3, by weight.

Another feature of embodiments of the present invention is that thecontent of tantalum may be reduced and the content of niobium may beincreased, such that niobium may be entirely substituted for tantalum ifdesired.

Another feature of embodiments of the present invention is that thecontents of tantalum and tungsten may be adjusted in such a manner thatresults in a combination of precipitation and solid solutionstrengthening.

Four experimental alloys having equiaxed grain structures were formedinto test articles using a casting method and comprising thecompositions given in Table 1 (in percent weight). Alloys 2 and 3 arevariations of the reference alloys, having ratios of aluminum totitanium near the upper limit (Alloy 2) and lower limit (Alloy 3) of theranges specified for the reference alloys. Alloys 1 and 4 arederivations of the reference alloys, having higher ratios of aluminum totitanium, as well as higher contents of tantalum and tungsten, than theranges specified for the reference alloys.

TABLE 1 Alloy 1 Alloy 2 Alloy 3 Alloy 4 Chromium (Cr) 13.9 13.9 13.914.0 Cobalt (Co) 9.5 9.5 9.5 9.5 Tungsten (W) 4.5 3.7 3.8 3.9 Titanium(Ti) 4.2 5.0 5.2 3.8 Aluminum (Al) 3.7 3.3 3.0 3.8 Tantalum (Ta) 3.4 2.92.8 3.4 Molybdenum (Mo) 1.6 1.5 1.5 1.5 Carbon (C) 0.1 0.1 0.1 0.1 Boron(B) 0.01 0.01 0.01 0.01 Niobium (Nb) 0.02 0.03 0.03 0.03 Hafnium (Hf)0.02 0.01 0.02 0.02 Zirconium (Zr) <0.01 <0.01 <0.01 <0.01 Nickel (Ni)Balance Balance Balance Balance

The microstructures of the four experimental alloys from Table 1 areshown in FIGS. 1 to 4, respectively. The microstructural evaluationsshowed that Alloy 1 had no visible Eta phase, a low fraction of eutecticphase, and a low fraction of carbides (FIG. 1); Alloy 2 had no visibleEta phase, an expected fraction of eutectic phase, and an expectedfraction of carbides (FIG. 2); Alloy 3 had visible Eta phase, anexpected fraction of eutectic phase, and an expected fraction ofcarbides (FIG. 3); and Alloy 4 had no visible Eta phase, a low fractionof eutectic phase, and a low fraction of carbides (FIG. 4).

Three other experimental alloys having directionally solidified grainstructures were formed into test articles using a casting method andcomprising the compositions given in Table 2 (in percent weight). Alloy5 is a derivation of the reference alloys, having a higher ratio ofaluminum to titanium, as well as higher contents of tantalum andtungsten, than the ranges specified for the reference alloys; whileAlloys 6 and 7 are variations of the reference alloys.

TABLE 2 Alloy 5 Alloy 6 Alloy 7 Chromium (Cr) 13.9 13.9 13.9 Cobalt (Co)9.5 9.5 9.5 Tungsten (W) 4.2 3.7 3.7 Titanium (Ti) 3.7 4.8 5.0 Aluminum(Al) 3.7 3.3 2.9 Tantalum (Ta) 3.2 2.6 2.6 Molybdenum (Mo) 1.5 1.5 1.5Carbon (C) 0.1 0.1 0.1 Boron (B) 0.01 0.01 0.01 Niobium (Nb) 0.02 0.020.02 Hafnium (Hf) 0.01 0.01 0.01 Zirconium (Zr) 0.002 0.002 0.002 Nickel(Ni) Balance Balance Balance

The microstructures of the three experimental alloys from Table 2 areshown in FIGS. 5 to 7, respectively. The microstructural evaluationsshowed that Alloy 5 had no visible Eta phase and a low fraction ofeutectic phase (FIG. 5); Alloy 6 had no visible Eta phase and anexpected fraction of eutectic phase (FIG. 6); and Alloy 7 had visibleEta phase and an expected fraction of eutectic phase (FIG. 7).

The results of representative mechanical and manufacturing evaluationsperformed on the test articles prepared from the four experimentalalloys from Table 1 are shown in FIGS. 8 to 10, respectively. Theseresults show that all four experimental alloys have tensile strengththat is above 90% of the tensile strength of the reference alloys atboth 20° C. and 760° C. (FIG. 8). The results also showed that the creeplife of Alloy 1 at 732° C. is generally equal to or greater than thecreep life of the reference alloys at 1.0% strain (FIG. 9), and thatAlloy 1 required less machining energy than Alloy 2 (a variation of thereference alloys) during milling (FIG. 12).

Summarizing, the present invention contemplates the use in a class ofnickel-base alloys of the elements aluminum, titanium, tantalum, andtungsten in a novel manner that advantageously improves bothmanufacturing yield and mechanical properties of alloys having superiormicrostructural stability and resistance to localized pitting and hotcorrosion in high temperature corrosive environments. The broad,preferred, and nominal compositions (by weight) of this class ofnickel-base alloys are summarized in Table 3.

TABLE 3 Broad Preferred Nominal 1 Nominal 2 Chromium (Cr) 13.7 to 14.313.7 to 14.3 13.9 13.9 Cobalt (Co)  5.0 to 10.0  5.0 to 10.0 9.5 9.5Tungsten (W) 3.5 to 5.2 4.0 to 4.6 4.5 4.2 Titanium (Ti) 2.8 to 5.2 3.6to 4.3 4.2 3.7 Aluminum (Al) 2.8 to 4.6 3.5 to 3.9 3.7 3.7 Tantalum (Ta)0.0 to 3.5 3.1 to 3.5 3.4 3.2 Molybdenum 1.0 to 1.7 1.0 to 1.7 1.6 1.5(Mo) Carbon (C) 0.08 to 0.13 0.08 to 0.13 0.1 0.1 Boron (B) 0.005 to0.02  0.005 to 0.02  0.01 0.01 Niobium (Nb) 0.0 to 1.5 0.0 to 1.5 0.020.02 Hafnium (Hf) 0.0 to 2.5 0.0 to 2.5 0.02 0.01 Zirconium (Zr)  0.0 to0.04  0.0 to 0.04 <0.01 0.002 Nickel (Ni) Balance Balance BalanceBalance

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralelements or steps, unless such exclusion is explicitly recited.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. An alloy comprising the following elements, by weight: a. about 13.7 to about 14.3 percent chromium, b. about 5.0 to about 10.0 percent cobalt, c. about 3.5 to about 5.2 percent tungsten, d. about 2.8 to about 5.2 percent titanium, e. about 2.8 to about 4.6 percent aluminum, f. about 0.0 to about 3.5 percent tantalum, g. about 1.0 to about 1.7 percent molybdenum, h. about 0.08 to about 0.13 percent carbon, i. about 0.005 to about 0.02 percent boron, j. about 0.0 to about 1.5 percent niobium, k. about 0.0 to about 2.5 percent hafnium, l. about 0.0 to about 0.04 percent zirconium, m. the balance substantially nickel.
 2. The alloy of claim 1, comprising about 4.0 to about 4.6 percent tungsten.
 3. The alloy of claim 1, comprising about 3.6 to about 4.3 percent titanium.
 4. The alloy of claim 1, comprising about 3.5 to about 3.9 percent aluminum.
 5. The alloy of claim 1, comprising about 3.1 to about 3.5 percent tantalum.
 6. The alloy of claim 1, comprising about 0.0 to about 1.5 percent niobium or about 0.0 to about 3.5 percent tantalum.
 7. The alloy of claim 1, wherein the ratio of percent aluminum to percent titanium is about 0.8 to about 1.0, by weight.
 8. An alloy comprising the following elements, by weight, and having about zero Eta phase (Ni₃Ti) and segregated titanium: a. about 13.7 to about 14.3 percent chromium, b. about 5.0 to about 10.0 percent cobalt, c. about 3.5 to about 5.2 percent tungsten, d. about 2.8 to about 5.2 percent titanium, e. about 2.8 to about 4.6 percent aluminum, f. about 0.0 to about 3.5 percent tantalum, g. about 1.0 to about 1.7 percent molybdenum, h. about 0.08 to about 0.13 percent carbon, i. about 0.005 to about 0.02 percent boron, j. about 0.0 to about 1.5 percent niobium, k. about 0.0 to about 2.5 percent hafnium, l. about 0.0 to about 0.04 percent zirconium, m. the balance substantially nickel.
 9. The alloy of claim 8, comprising about 4.0 to about 4.6 percent tungsten.
 10. The alloy of claim 8, comprising about 3.6 to about 4.3 percent titanium.
 11. The alloy of claim 8, comprising about 3.5 to about 3.9 percent aluminum.
 12. The alloy of claim 8, comprising about 3.1 to about 3.5 percent tantalum.
 13. The alloy of claim 8, comprising about 0.0 to about 1.5 percent niobium or about 0.0 to about 3.5 percent tantalum.
 14. The alloy of claim 8, wherein the ratio of percent aluminum to percent titanium is about 0.8 to about 1.0, by weight.
 15. An alloy comprising the following elements, by weight: a. about 13.9 percent chromium, b. about 9.5 percent cobalt, c. about 4.5 percent tungsten, d. about 4.2 percent titanium, e. about 3.7 percent aluminum, f. about 3.4 percent tantalum, g. about 1.6 percent molybdenum, h. about 0.1 percent carbon, i. about 0.01 percent boron, j. less than 0.01 percent zirconium, k. the balance substantially nickel.
 16. An alloy comprising the following elements, by weight: a. about 13.9 percent chromium, b. about 9.5 percent cobalt, c. about 4.2 percent tungsten, d. about 3.7 percent titanium, e. about 3.7 percent aluminum, f. about 3.2 percent tantalum, g. about 1.5 percent molybdenum, h. about 0.1 percent carbon, i. about 0.01 percent boron, j. about 0.002 percent zirconium, k. the balance substantially nickel.
 17. An article of manufacture that may be used in a gas turbine and is formed from an alloy comprising the following elements, by weight: a. about 13.7 to about 14.3 percent chromium, b. about 5.0 to about 10.0 percent cobalt, c. about 3.5 to about 5.2 percent tungsten, d. about 2.8 to about 5.2 percent titanium, e. about 2.8 to about 4.6 percent aluminum, f. about 0.0 to about 3.5 percent tantalum, g. about 1.0 to about 1.7 percent molybdenum, h. about 0.08 to about 0.13 percent carbon, i. about 0.005 to about 0.02 percent boron, j. about 0.0 to about 1.5 percent niobium, k. about 0.0 to about 2.5 percent hafnium, l. about 0.0 to about 0.04 percent zirconium, m. the balance substantially nickel.
 18. The alloy of claim 17, comprising about 4.0 to about 4.6 percent tungsten.
 19. The alloy of claim 17, comprising about 3.6 to about 4.3 percent titanium.
 20. The alloy of claim 17, comprising about 3.5 to about 3.9 percent aluminum.
 21. The alloy of claim 17, comprising about 3.1 to about 3.5 percent tantalum.
 22. The alloy of claim 17, comprising about 0.0 to about 1.5 percent niobium or about 0.0 to about 3.5 percent tantalum.
 23. The alloy of claim 17, wherein the ratio of percent aluminum to percent titanium is about 0.8 to about 1.0, by weight.
 24. The article of claim 17, wherein the method of forming is casting.
 25. The article of claim 24, wherein the method of forming is casting performed in such a manner as to produce an equiaxed grain structure.
 26. The article of claim 24, wherein the method of forming is casting performed in such a manner as to produce a directionally solidified grain structure.
 27. The article of claim 24, wherein the method of forming is casting performed in such a manner as to produce a single crystal grain structure.
 28. The article of claim 17, wherein that article is a gas turbine bucket or other form of rotating airfoil located in the turbine hot section.
 29. The article of claim 17, wherein that article is a gas turbine nozzle or other form of stationary airfoil located in the turbine hot section.
 30. An article that may be used in a gas turbine and is formed from an alloy comprising the following elements, by weight: a. about 13.9 percent chromium, b. about 9.5 percent cobalt, c. about 4.5 percent tungsten, d. about 4.2 percent titanium, e. about 3.7 percent aluminum, f. about 3.4 percent tantalum, g. about 1.6 percent molybdenum, h. about 0.1 percent carbon, i. about 0.01 percent boron, j. less than 0.01 percent zirconium, k. the balance substantially nickel.
 31. The article of claim 30, wherein the method of forming is casting.
 32. The article of claim 31, wherein the method of forming is casting performed in such a manner as to produce an equiaxed grain structure.
 33. The article of claim 30, wherein that article is a gas turbine bucket or other form of rotating airfoil located in the turbine hot section.
 34. The article of claim 30, wherein that article is a gas turbine nozzle or other form of stationary airfoil located in the turbine hot section.
 35. An article that may be used in a gas turbine and is formed from an alloy comprising the following elements, by weight: a. about 13.9 percent chromium, b. about 9.5 percent cobalt, c. about 4.2 percent tungsten, d. about 3.7 percent titanium, e. about 3.7 percent aluminum, f. about 3.2 percent tantalum, g. about 1.5 percent molybdenum, h. about 0.1 percent carbon, i. about 0.01 percent boron, j. about 0.002 percent zirconium, k. the balance substantially nickel.
 36. The article of claim 35, wherein the method of forming is casting.
 37. The article of claim 36, wherein the method of forming is casting performed in such a manner as to produce a directionally solidified grain structure.
 38. The article of claim 35, wherein that article is a gas turbine bucket or other form of rotating airfoil located in the turbine hot section.
 39. The article of claim 35, wherein that article is a gas turbine nozzle or other form of stationary airfoil located in the turbine hot section. 